The Earth’s inner core is incredibly difficult to study because it is buried under thousands of miles of rock. New seismic studies suggest it’s not just a solid ball of iron, as was believed, but there could be pockets of liquid iron everywhere.
Like flakes that settle at the bottom of a snow globe, iron and other heavy metals tend to sink through the lighter molten rock and end up concentrated in the earth’s core. But exactly what form the iron takes when it gets there remains up for debate. For a long time it was believed to be liquid, due to the extremely high temperatures it encounters there.
But in the 1930s, scientists began probing the core by studying seismic waves from earthquakes. By watching how these bounce back to sensors, it’s possible to get an idea of the types of material they move through at different stages. These studies revealed that the inner core was a solid ball of iron.
However, according to a new study from the University of Utah, it doesn’t always have the same consistency. The team used data collected by the International Monitoring System (IMS), a network of sensors originally set up around the world to detect illegal underground nuclear explosions. They analyzed seismic waves from 2,455 earthquakes of magnitude 5.7 and above, and used them to map the inner core’s internal structure in greater detail.
The scattering pattern they picked up revealed that the core is not the same everywhere. It’s mostly solid, but appears to contain what the researchers describe as a tapestry of different “substances,” a product of its growth over time.
“We think this tissue is related to how fast the inner core grew,” says Keith Koper, superintendent of the study. “A long time ago, the inner core grew very quickly. It reached equilibrium and then began to grow much more slowly. Not all of the iron solidified, so some liquid iron could get trapped.”
Other studies have shown that the inner core may be solid but soft, or made of a strange superionic alloy that exists in a state of matter somewhere between a liquid and a solid. Gaining a better understanding of what’s going on down there could help us learn more about our planet’s history, how its protective magnetic field is formed and maintained, and could help us figure out if other planets are habitable.
The new research is published in the journal Nature.
Source: University of Utah
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